Microjoule-energy, 1 MHz repetition rate pulses from all-fiber-integrated nonlinear chirped-pulse amplifier

We demonstrate generation of pulses with up to 4 microJ energy at 1 MHz repetition rate through nonlinear chirped-pulse amplification in an entirely fiber-integrated amplifier, seeded by a fiber oscillator. The peak power and the estimated nonlinear phase shift of the amplified pulses are as much as 57 kW and 22pi, respectively. The shortest compressed pulse duration of 140 fs is obtained for 3.1 microJ of uncompressed amplifier output energy at 18pi of nonlinear phase shift. At 4 microJ of energy, the nonlinear phase shift is 22pi and compression leads to 170-fs-long pulses. Numerical simulations are utilized to model the experiments and identify the limitations. Amplification is ultimately limited by the onset of Raman amplification of the longer edge of the spectrum with an uncompressible phase profile.